Apple Final Cut Pro 5 - Manual (Page 894)

Chapter 6 Using the Audio Mixer 107
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You can even adjust a fader to a new position while it is moving. For example, if a fader
on the control surface is slowly moving down from a 0 dB keyframe to a –60 dB
keyframe, you can move the motorized fader up to +12 dB, creating new keyframes.
When you release the fader, it returns to its trajectory moving toward the –60 dB keyframe.